As is known, the heat engine of a motor vehicle is cooled by a cooling system which uses as a coolant fluid a mixture of water/ethylene glycol and provides for an expansion tank fixed to a support structure placed in the engine compartment of the motor vehicle.
The expansion tank is a container which communicates with the exterior via a series of inlet and outlet mouths. Said mouths are provided at respective sleeves and collars which protrude from the container and are made of plastic material, in one piece with the container itself. Then, during the installation of the cooling system, corresponding piping is fitted on said collars to connect the inside of the container with the motor and with the radiator.
In some solutions, at the inlet mouth, the expansion tank is provided with a cylindrical bushing, defining an insert that has a radial thickness of about 0.5 mm and is fixed inside the plastic collar, to reduce the transmission of heat from the coolant fluid to said collar. According to the European patent application 16162753.4, in the name of the same applicant, in particular, it is provided that said insert is made of plastic and is snap-fixed to the collar.
In the known solutions, immediately after turning off the engine, a gurgling sound is generally perceived coming from the expansion tank. This gurgling is essentially due to the bubbles of vapor and coolant fluid which continue, even if for a short time, to enter the container from the inlet mouth, due to the inertia of the coolant fluid in the cooling system and the high temperatures in the return line from the engine to the expansion tank.
This gurgling is relatively annoying, particularly in solutions where the engine is equipped with the so-called “start-stop” function and therefore subject to a relatively high number of shut-downs.